1. Field of the Invention
This invention relates to torque converter drives and more particularly to such drives utilizing a parallel arrangement of a viscous drive and friction clutch to bypass the torque converter fluid drive.
2. Description of the Prior Art
To improve the efficiency of hydrodynamic type transmissions, the use of torque converter bypass devices is increasing. These devices include friction clutch designs, which lock up at higher speeds to improve the efficiency of the transmission at higher speeds where torque multiplication is not required. The friction clutches wear when slipping upon initial engagement. Friction clutches also inherently prevent utilization of the high damping capacity of the torque converter. Therefore, a vibration damper must be utilized with the torque converter clutch in an effort to decrease the transmission of engine torsional vibrations. Other bypass devices include viscous couplings, which provide damping and which reduce the wear concerns of the friction clutch, but the viscous couplings generally are not as efficient because slippage exists with the viscous coupling. Finally, devices have been made, which combine a friction clutch in series with a viscous coupling. In such designs, the viscous coupling acts as a damper to reduce the NVH concerns and reduce the wear of the friction surfaces because the torque from the friction clutch passes through the viscous coupling. However, with such designs the friction clutch must be engaged for the viscous coupling to be effective. Thus the torque path travels through both the friction clutch and the viscous coupling; therefore the shortcomings of each device are present in such a device, as the friction clutch will still wear and the viscous coupling will still slip to some extent. It would therefore be desirable to have a bypass clutch which provides a friction clutch and viscous drive, each of which provide an independent bypass torque path for a torque converter.